In the fabrication of semiconductor wafers, one recurring problem has been temperature measurement and control. When processing a semiconductor substrate, the temperature of the to side of the substrate being processed is of critical importance. Overheating can cause dopants to permeate subjacent layers, and under-heating can produces layers which are unreliable and subject to lower tolerances. In this light, several solutions have been put forth to gauge the substrate's temperature to avoid overheating and underheating, and thus provide a uniform ramp up, steady state and/or ramp down cycle.
Referring to FIG. 1, a pyrometric system for measuring the temperature of a semiconductor substrate in a chamber known in the art is illustrated. In this system, a lamp 100 is employed to heat substrate 110. Substrate 110 is situated within chamber 120, and the substrate's top side 115 is positioned in association with lamp 100 accordingly. To maintain the stability of substrate 100, a series of supports, 130 and 130', emanate from the bottom of chamber 120. A sensor (not shown) is positioned between supports 130 and 130' and in association with the underside 116 to sense the temperature of the underside 116 of substrate 110.
The pyrometric system depicted in FIG. 1 is inadequate for precise temperature measurements. By measuring the underside of the substrate, this approach yields only an approximate measurement of the top side at best. Moreover, the underside is not traditionally processed, and as such, measurements with regards to that portion of the wafer are superfluous.
Referring to FIG. 2, a system configuration for measuring the temperature of a semiconductor substrate in a chamber known in the art is illustrated. In this system, a substrate 210, positioned within a chamber 220, is positioned in association with lamp 200 for heating purposes. Instead of the approach of FIG. 1, here a sensor 230, positioned on the side of substrate 210, is employed to detect the thermal expansion of substrate 210, which is directly translatable to the substrate's temperature.
However, the system depicted in FIG. 2 also has several shortcomings. Firstly, though a relationship exists between thermal expansion and temperature, an accurate temperature measurement is formidable to obtain because of the difficulties in fabricating sufficiently sensitive sensors to detect expansion. Second, several layers are formed superjacent the substrate, with each layer having a different thermal coefficient. As such, most measurements of the thermal expansion of the substrate are inaccurate. Third, in actual semiconductor manufacturing, substrate's are exposed to several thermal steps. Thus, actual measurements of expansion are transitory.